We continue our focus on the HIV-associated oncogenic human gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV, HHV-8). In addition to Kaposis sarcoma of endothelial cells, KSHV is causatively linked to two B-cell lymphoproliferative disorders: multicentric Castlemans disease and primary effusion lymphoma. The mechanisms underlying KSHV tropism for the major cell types associated with pathology are poorly understood. Isolation of a KSHV stably infected endothelial cell line inducible for infectious virus Based on our earlier identification of a human B cell line (MC116) with unusual susceptibility to KSHV infection, we have found that the viral k8.1A glycoprotein plays a critical role in B cell infection. This stands in contrast to other non-B cell targets, for which k8.1A is known to be dispensable. We have also identified a second route by which KSHV infects some other human B cell lines, namely antibody-mediated infection mediated by the Fc receptor on the B cell surface. As a component of our approach to elucidating molecular mechanisms underlying KSHV tropism for distinct target cells, we have devised efficient systems for KSHV infectious virus production from two relevant cell types: the MC116 human B cell line, and human telomerase-immortalized microvascular endothelial (TIME) cells. Specifically, we have generated stable chronically infected cell lines from each of these parental cells, in which a recombinant KSHV genome can be induced upon doxycycline activation of the lytic switch RTA protein (under control of the Tet operator). Abundant infectious virus is produced from both cell types. An alternative non-specific inducer, sodium butyrate, can also be used to stimulate virus production. Most interestingly, we have found that the virus generated from these cell lines displays infection widely differing tropisms for different target cells, dependent on both the cell type from which the virus originated, and the mode of induction. These chronically infected cell systems represent valuable tools for studying viral and cellular determinants underlying KSHV tropism for critical cell types involved in diseases caused by this human pathogen.